Solar kudzu: How Rule 21 is shaping solar’s growth in California and beyond

May 11, 2016 Kathie Zipp :

By Harumi McClure, managing director of Tabuchi America

California has long been a leader in solar policy. And as history has shown us time and time again, global trends– from Facebook to electric cars–tend to start in California before taking over the world.
Innovative policies have incentivized massive solar growth in the Golden State, amounting to a total of 13,243 MW of installed solar in 2015–enough to power about 3.3 million homes. With this influx of solar comes challenges balancing supply and demand, maintaining voltage requirements and sidestepping the famous “duck curve” that threatens to further throw the grid into knots. One of California’s latest solar policies, Rule 21 is a set of solar interconnection requirements from California regulators intended to smooth out these solar challenges.

Buried in extensive technical language, Rule 21 can be difficult for even the most hardened policy wonk to understand. The short and sweet is that Rule 21 mandates that solar installers deploy smart inverters to residential and commercial solar systems and will require new systems to have smart capabilities when connecting to the grid. That means that utilities will have more control over how and when solar power flows onto the grid.
Rule 21 revisions are expected to roll out this June and will change the way solar energy flows onto the grid. And it’s very likely a harbinger of what’s to come across the country–and beyond.

The rise of solar kudzu
Rule 21 was written in the early 1980s, when solar was essentially an expensive fad and there was little sign of the massive growth and plummeting costs we see today. Regulators have adjusted Rule 21 to pull off the balancing act of maintaining grid stability and reliability while inviting more solar power onto the grid.

An analogy can help. Kudzu is a beautiful vine that smells lovely and is quite pleasing to the eye. However, left unchecked, kudzu will grow rapaciously, destroying other plant life and leaving the best-laid gardening plans in shambles. To maintain a beautiful energy garden—with plenty of solar, but also account for other energy sources that, at least for now, comprise the grid—we must manage growing solar “kudzu” on a comprehensive, systemic level.
As many embrace organic growth, some have come out against Rule 21 as overkill. They argue that it adds cost and complexity to solar installations, while giving power over solar to the group—utilities—which have historically been most likely to block solar policy.
It’s important to remember that today’s connected world cannot withstand power outages. What used to be a minor inconvenience can now be the difference between life and death, or profit and bankruptcy. Growing solar kudzu, if left to its own devices, could potentially overwhelm the grid and lead to disastrous outcomes.

Smart inverters to the rescue
Fortunately, managing solar kudzu with innovations sparked by Rule 21 can not only overcome objections but also open up massive new markets for solar power. It all starts with smart inverters, which can be controlled to manage the flow of solar power onto the grid.

When the first phase of modifications to Rule 21 are ratified this June, new solar systems connecting to the grid will be required to perform seven autonomous functions in reactive power compensation, voltage and frequency ride-through, and real-time data connectivity. Essentially, this puts the amount of power, the quality of power and when the power is provided under utility control.
More revisions are on the horizon. The second phase of modifications require distributed energy resources to communicate with the grid operator, with further phases under discussion. Rule 21 will bring inverter technology decidedly into the smart capabilities era and manufacturers are designing systems in light of these parameters.

Despite concerns of some solar advocates, smart inverters represent a practical solution to the challenge of solar kudzu. A report released in 2015 by the Solar Electric Power Association and the Electric Power Research Institute found that autonomous inverter grid support functions could be deployed at a low cost and that retrofitting inverters for advanced capabilities can be effectively managed by utilities.

Smart inverters aren’t a theoretical exercise. The technology has already been proven to help stabilize the grid in countries with high solar penetration, such as Germany and Japan. In fact, my company, Tabuchi Electric, developed grid-friendly smart inverters in the wake of Fukushima to help Japanese utilities manage the sudden influx of solar that came online to replace nuclear power. With our help, Japan responsibly scaled and managed solar kudzu, and is now a global solar leader.
Today, some inverter manufacturers sell inverters with smart function capabilities turned on in one country, and switched off in others like the United States. Modifications to Rule 21 will enable these latent capabilities to ensure distributed power integrates smoothly onto the grid.

Next, we can look to forthcoming generations of smart inverters to add additional battery capabilities such as Tabuchi Electric’s solar-plus-storage-system. Our inverters aren’t just smart but are also integrated with battery storage in an all-in-one, turnkey solution. Storage improves all of the seven autonomous functions under Rule 21 while offering myriad benefits to solar customers as well as utilities. When a standard inverter shuts off for safety reasons, or when cloud cover reduces solar generation, a smart inverter with a battery can provide uninterrupted power that can help to balance the grid.

Bridging the gap
Much has been made of the perceived rivalry between solar companies and utilities. Smart inverters can bridge that gap by delivering a predictable solar load that meets precise utility specifications. By better managing the solar kudzu, solar companies can circumvent destabilization objections and quickly scale, as we did in Japan.
Rule 21 is just the beginning. As more states — and countries — face the growth of solar kudzu, we’ll see more policy solutions spring up to deploy smart inverters and more new technologies to address a range of grid stability and safety concerns. Utilities in states with high solar penetration like Hawaii, Arizona and Utah are already following California’s rollout of smart inverter standards. The transition to a new generation of solar technologies, guided by veteran manufacturers and lessons learned from other countries, will bring a more equitable and efficient energy system to the United States, and promise to help solar scale to brave new heights.